Core failure modes in composite sandwich beams

Core failure modes were studied in composite sandwich beams under three-point bending and in cantilever beams under end loading. The beams consisted of unidirectional carbon/epoxy face sheets and a variety of core materials, including aluminum honeycomb, PVC closed-cell foams, polyurethane foam and balsa wood. The constituent materials were fully characterized and in the case of the core materials, failure envelopes were developed for biaxial states of stress. Deformation and failure mechanisms were studied experimentally by means of moiré gratings and birefringent coatings. Results were obtained for stress (strain) distributions in the linear and nonlinear/plastic range of the core, critical failure loads and their dependence on geometrical dimensions, material parameters and loading conditions.